If
XTranslateCoordinates returns True, it takes the src_x and src_y coordinates
relative to the source window's origin and returns these coordinates to
dest_x_return and dest_y_return relative to the destination window's origin.
If XTranslateCoordinates returns False, src_w and dest_w are on different
screens, and dest_x_return and dest_y_return are zero. If the coordinates
are contained in a mapped child of dest_w, that child is returned to child_return.
Otherwise, child_return is set to None.